init: Add support for zstd compressed kernel

LZMA		= lzma

LZ4		= lz4c

XZ		= xz

ZSTD		= zstd

CHECKFLAGS     := -D__linux__ -Dlinux -D__STDC__ -Dunix -D__unix__ \

		  -Wbitwise -Wno-return-void -Wno-unknown-attribute $(CF)

export ARCH SRCARCH CONFIG_SHELL BASH HOSTCC KBUILD_HOSTCFLAGS CROSS_COMPILE LD CC

export CPP AR NM STRIP OBJCOPY OBJDUMP OBJSIZE READELF PAHOLE LEX YACC AWK INSTALLKERNEL

export PERL PYTHON PYTHON3 CHECK CHECKFLAGS MAKE UTS_MACHINE HOSTCXX

export KGZIP KBZIP2 KLZOP LZMA LZ4 XZ

export KGZIP KBZIP2 KLZOP LZMA LZ4 XZ ZSTD

export KBUILD_HOSTCXXFLAGS KBUILD_HOSTLDFLAGS KBUILD_HOSTLDLIBS LDFLAGS_MODULE

export KBUILD_CPPFLAGS NOSTDINC_FLAGS LINUXINCLUDE OBJCOPYFLAGS KBUILD_LDFLAGS

config HAVE_KERNEL_LZ4

	bool

config HAVE_KERNEL_ZSTD

	bool

config HAVE_KERNEL_UNCOMPRESSED

	bool

choice

	prompt "Kernel compression mode"

	default KERNEL_GZIP

	depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO || HAVE_KERNEL_LZ4 || HAVE_KERNEL_UNCOMPRESSED

	depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO || HAVE_KERNEL_LZ4 || HAVE_KERNEL_ZSTD || HAVE_KERNEL_UNCOMPRESSED

	help

	  The linux kernel is a kind of self-extracting executable.

	  Several compression algorithms are available, which differ

	  is about 8% bigger than LZO. But the decompression speed is

	  faster than LZO.

config KERNEL_ZSTD

	bool "ZSTD"

	depends on HAVE_KERNEL_ZSTD

	help

	  ZSTD is a compression algorithm targeting intermediate compression

	  with fast decompression speed. It will compress better than GZIP and

	  decompress around the same speed as LZO, but slower than LZ4. You

	  will need at least 192 KB RAM or more for booting. The zstd command

	  line tool is required for compression.

config KERNEL_UNCOMPRESSED

	bool "None"

	depends on HAVE_KERNEL_UNCOMPRESSED

quiet_cmd_xzmisc = XZMISC  $@

      cmd_xzmisc = cat $(real-prereqs) | $(XZ) --check=crc32 --lzma2=dict=1MiB > $@

# ZSTD

# ---------------------------------------------------------------------------

# Appends the uncompressed size of the data using size_append. The .zst

# format has the size information available at the beginning of the file too,

# but it's in a more complex format and it's good to avoid changing the part

# of the boot code that reads the uncompressed size.

#

# Note that the bytes added by size_append will make the zstd tool think that

# the file is corrupt. This is expected.

#

# zstd uses a maximum window size of 8 MB. zstd22 uses a maximum window size of

# 128 MB. zstd22 is used for kernel compression because it is decompressed in a

# single pass, so zstd doesn't need to allocate a window buffer. When streaming

# decompression is used, like initramfs decompression, zstd22 should likely not

# be used because it would require zstd to allocate a 128 MB buffer.

quiet_cmd_zstd = ZSTD    $@

      cmd_zstd = { cat $(real-prereqs) | $(ZSTD) -19; $(size_append); } > $@

quiet_cmd_zstd22 = ZSTD22  $@

      cmd_zstd22 = { cat $(real-prereqs) | $(ZSTD) -22 --ultra; $(size_append); } > $@

# ASM offsets

# ---------------------------------------------------------------------------